Ink printers, often also referred to as inkjet printers, comprising one or more print heads are known in general and are used for example in transaction printing for producing personalised brochures. When the printing operation is interrupted, for example in order for the paper to be changed or in start-stop operation, there is the risk of ink residues contaminating the outlet region of the print heads and thus blocking individual outlet openings. In order to provide high print quality when using inkjet printers of this type, the print heads of said printers therefore have to be cleaned at regular intervals and in accordance with the printer status. It is important to clean the nozzles of the print heads in particular before starting up an inkjet printer which has not been used for some time.
The present invention relates in particular to a method for effectively cleaning inkjet printer heads, in particular inkjet printer heads of the type in which paper dust and ink residues have built up. In order for such inkjet print head nozzles which have been blocked by a mixture of ink and paper dust to be fully functional again, and for high quality to be ensured in inkjet printers, said nozzles have to be cleaned. There are various possibilities for the cleaning in this case:                Rinsing the print heads and/or the nozzles provided therein inside the printer using the ink from the inkjet printing system. Thoroughly rinsing the print heads and, in this case, in particular the outlet openings of the print heads, is generally known as “purging”.        Rinsing the print heads inside or outside the printer using a standard cleaning fluid with and without increased rinsing pressure and/or increased rinsing time. The standard cleaning fluid is typically provided by the manufacturer of the inkjet printer ink.        Manually cleaning using lint-free cloths and standard cleaning fluid.        
U.S. Pat. No. 6,164,752 describes an ink printing device, in which, for thoroughly rinsing a print head, the print head is firstly positioned in a rinsing position, in which a rinsing cap covers the outlet nozzles. Ink is then sucked through the nozzles by applying a pulsed negative pressure via a suction cap.
U.S. Pat. No. 7,118,189 B2 describes a rinsing device for an ink printing device, in which ink is squeezed through the nozzles in a pulsed manner by means of an ink squeezing valve arranged in the ink supply line.
It is common to all the above-mentioned methods that the contaminants and blockages cannot be satisfactorily cleared from the nozzles of the print heads using said methods. It is also problematic that the blockage, which generally consists of a mixture of ink and paper dust, cannot be readily rinsed out of the nozzles, since the paper dust gives the blockage increased stability.
Conventional cleaning agents comprising surfactants or similar detergent substances are able to bind and thus clean away the ink. However, the combination of paper dust and ink cannot be cleared, or cannot be satisfactorily cleared, using cleaning agents of this type.